1. Field of the Invention
The present invention relates to an imaging filter and more particularly to an imaging filter for use with a search radar system which detects and tracks various targets including moving targets while suppressing false detection without relying on a straight line trajectory of the target.
2. Description of the Prior Art
Various imaging systems are known and used in a wide variety of applications. For example, search radar systems are known for imaging targets in a particular region of interest. Examples of such search radar systems are disclosed in U.S. Pat. Nos. 3,670,331; 3,680,100; 4,542,382 and 5,311,187; hereby incorporated by reference. Such search radar systems normally include a phased array antenna system or a mechanically rotatable antenna which sweeps a predetermined region of interest. The search radar systems are used for detecting and tracking various targets including moving targets and provide the range, azimuth and elevation of such targets in the predetermined region of interest as a function of time.
An important consideration in such search radar systems is the ability to suppress false detections. In general, radar systems including search radar systems normally compare the radiation reflected back to the radar system to a predetermined threshold. Reflected radiation having an energy level greater than the threshold is assumed to be reflected from a target and displayed or further processed. In order to further enhance the ability to detect and track moving targets and suppress noise, various other techniques have been developed. For example, "SEARCH RADAR DETECTION AND TRACK WITH THE HOUGH TRANSFORM PART I: SYSTEM CONCEPT", by B. D. Carlson, E. D. Evans and S L. Wilson,--IEEE Transactions on Aerospace and Electronics Systems, Vol. 30, No. 1, January 1994, pgs. 102-108; "SEARCH RADAR DETECTION AND TRACK WITH THE HOUGH TRANSFORM PART II: DETECTION STATISTICS", by B. D. Carlson, E. D. Evans and S. L. Wilson, IEEE Transactions on Aerospace and Electronics Systems, Vol. 30, No. 1, January 1994, pgs. 109-115, and "SEARCH RADAR DETECTION AND TRACK WITH THE HOUGH TRANSFORM PART III: DETECTION PERFORMANCE WITH BINARY INTEGRATION", by B. D. Carlson, E. D. Evans and S. L. Wilson, IEEE Transactions on Aerospace and Electronics Systems, Vol. 30, No. 1, January 1994, pgs. 116-125 disclose a processing technique in which the target trajectories are modeled as straight lines or low order polynomial curves. Any reflected radar energy greater than a threshold is then transformed into a parameter space where voting takes place based upon the expected straight line trajectory of the target. The parameters that receive the most votes are considered to represent the actual targets. Unfortunately, such a processing technique does not apply to target trajectories which do not fit the polynomial used as the model. For example, accurate tracking of people in a cluttered ground environment would produce erratic trajectories which would not fit such a model. As such, the processing technique as discussed in the above mentioned articles has limited utility.